Preparation of wood for bending



May 12, 1964 PREPARATION OF WOOD FOR BENDING Filed Jan. 29, 1962 N. TURNER /N VE N TOP Norman Turner 3,132,674 PREPARATION OF WOOD FOR BENDING Norman Turner, Aylesbury, England, assignor to National Research Development Corporation, London, England,

a British corporation Filed Jan. 29, 1962, Ser. No. 169,367 Claims priority, application Great Britain Feb. 3, 1961 4 Claims. (Cl. 144-327) The invention relates to the preparation of wood for bending by a combination of a hot softening treatment such as steaming or boiling and compression along the grain (longitudinally) by which the wood is rendered considerably more flexible.

In the usual procedure for this purpose the wood is steamed, longitudinally compressed and then clamped and maintained under constraint until it has cooled. The clamps are then released and the wood which has been rendered flexible, is ready for bending.

The invention is based upon the discovery that good results can be obtained if the steamed and compressed wood is released while it is still hot from the steam, that is to say while the temperature of the wood is still substantially above that of the surrounding atmosphere, and allowed to cool while free from any longitudinal compressive force. It is possible to carry out bending immediately after release of the longitudinal compression or some days or even weeks later. The wood may be resteamed to increase flexibility still further.

The invention may be used to render flexible wood which is to be used directly or to improve the flexibility of wood which is to be made into plywood, laminated wood or even block board. For this latter purpose a log of wood is steamed or boiled in the usual manner before conversion into veneer. After reduction to a clean cylindrical form the wood is enclosed in a suitable cylindrical casing with a sliding plunger and compressed, for example in a hydraulic press. The pressure being released the wood can be converted, immediately if desired, into veneer by the usual technique.

In accordance with the invention the wood to be rendered flexible will usually be compressed by from a fifteen to thirty percent of the initial steamed length and preferably by at least twenty percent. It has been found that compression of twenty percent requires the application of a pressure of 4,000 lbs. per square inch or more for ash. Preferably the compressed timber should be at a moisture content of not less than eighteen percent and preferably twenty percent or more before being bent to the final shape required.

In bending wood which has been rendered flexible in accordance with the invention, it is found that the setting time can be reduced to as little as one-third of that required to set the uncompressed wood.

In order that the invention may be thoroughly understood a process in accordance with it, by which wood is prepared for the particular purposes of bending into spade handles, will be described, in some detail, by way of example, with reference to the accompanying drawing, in which:

FIGURE 1 shows a finished spade handle;

FIGURE 2 shows the prepared wood from which the handle of FIGURE 1 is made;

FIGURE 3 is a diagrammatic plan view, partly in section, showing apparatus for compressing wood in accordance with the invention; and

FIGURE 4 is a similar view showing the wood under compression.

The invention is described in its application to the fabrication of all-wood split Y-D ash spade handles such as the handle shown in FIGURE 1 of the accompanying drawing. Round pieces of wood of the appropriate United. States Patent 0 length to form a shaft 12 and the handle 10 are rendered flexible by steaming and compression, the ends on which the handles are to be formed are tapered, as at 14 in FIGURE 2, divided by a saw cut 16, transversely rivetted by a rivet 18, to prevent splitting, and the two halves 20 and 22 are then bent to the required shape and held until set in a suitable mould (not shown). When set and withdrawn from the mould the shaped handle is fitted with the usual cross piece 24 (FIGURE 1). 1

The wood to form the handle 10 is prepared for bending in accordance with this invention, in the following manner, described with reference to FIGURES 3 and 4.

The end of each piece of wood 1012 which is to be shaped into a handle 10 is softened by steaming or boiling in the usual way. The length which is so softened is indicated in FIGURES 3 and 4 by the transverse broken lines 8-8. The complete handle and shaft 10-12 is then slid into a fitting tube 26, say of 10 gauge brass reinforced at the points 27, 27, 28, 28, by external flanges, and there subjected to a heavy axial load applied through a sliding fit plunger 30 of mild steel carried on the piston rod 32 of a hydraulic cylinder 34. The plunger 30 is a sliding fit within the tube 26 the other end of which is closed by a heavy stop. The tube 26, the hydraulic cylinder 34, and the stop 36 are all mounted on a heavy bed plate 38.

By this apparatus there is induced in the wood a high compressive strain in the steamed part which is to form the handle 10. For example under a load of 4,000 lbs. per square inch the residual compression in ash after the load has been released might amount to some 5 /2% of the steamed length of the wood.

The degree of compression is regulated in the apparatus shown in FIGURES 3 and 4 by a microswitch 40 'mounted on the bed plate 38, the position of which can be adjusted by means not shown, so that when the required degree of compression has been attained, a projection 42 on the plunger 30 closes the microswitch, thereby to close a valve 44 in the hydraulic supply to the cylinder 34. The connection between the microswitch 40 and the valve 44 may be of any conventional nature and is not illustrated in detail.-

After compression the axial load is released permitting a partial recovery of the compressed wood, and the Wood 1012 is withdrawn from the tube 26 and set aside to cool.

The cooled handle is then tapered, saw cut, rivetted with the mild steel rivet 18 shown in FIGURES l and 2, and bent to the shape shown in FIGURE 1, in a mould of conventional design, without further treatment. It is found that the handle 10 will set in the mould in about one and a half hours in an oven at 212 F. dry heat, which is substantially less than the time required when conventional steaming is employed.

In the process described, rejects resulting from breakages during bending are markedly reduced, no unnecessary time is spent in clamping the compressed wood and no clamps have to be employed, thus making possible a reduction in the cost of preparing handles for shaping.

The usefulness of the process is by not means confined to the particular purpose of making wooden spade handles in the manner described above, and the detailed description is only given to illustrate the value of the process according to the invention for preparing wood for bending.

I claim:

1. A method of preparing wood for bending which comprises softening the wood with heat and moisture, compressing the steamed wood along the grain, releasing the wood while still hot from the softening process, and allowing it to cool while free from any longitudinal compressive force.

2. A method according to claim 1 during which the wood is compressed by at least twenty percent of its initial softened length.

3. A method of bending Wood which comprises softening the wood with heat and moisture, compressing the softened wood along the grain, releasing the wood while still hot from the softening process, and allowing it to cool while free from any longitudinal compressive force, reheating and moistening the wood to increase flexibility still further, bending the wood to the desired shape and setting it in that shape.

4. A method of bending wood according to claim 3 in which the compressed wood is at a moisture content of not less than eighteen percent before being bent to desire shape.

ReferencesCited in the file of this patent UNITED STATES PATENTS 650,269 Ordway May 22, 1900 992,114 Curry May 9, 1911 FOREIGN PATENTS 48,234 Sweden Dec. 29, 1920 414,639 Great Britain Mar. 13, 1934 r 409,347 Great Britain Apr. 30, 1934 

1. A METHOD OF PREPARING WOOD FOR BENDING WHICH COMPRISES SOFTENING THE WOOD WITH HEAT AND MOISTURE, COMPRESSING THE STEAMED WOOD ALONG THE GRAIN, RELEASING THE WOOD WHILE STILL HOT FROM THE SOFTENING PROCESS, AND ALLOWING IT TO COOL WHILE FREE FROM ANY LONGITUDINAL COMPRESSIVE FORCE. 